IrRegular Expressions

At this moment there was a loud ring at the bell, and I could
hear Mrs. Hudson, our landlady, raising her voice in a wail of
expostulation and dismay.

"By heaven, Holmes," I said, half rising, "I believe that
they are really after us."

"No, it's not quite so bad as that. It is the unofficial
force, -- the Baker Street irregulars."

A fully portable and efficient R[4567]RS implementation of regular
expressions, supporting both POSIX syntax with various (irregular)
PCRE extensions, as well as SCSH's SRE syntax, with various aliases
for commonly used patterns. DFA matching is used when possible,
otherwise a closure-compiled NFA approach is used. The library makes
no assumptions about the encoding of strings or range of characters
and can thus be used in Unicode-aware Scheme implementations.
Matching may be performed over standard Scheme strings, or over
arbitrarily chunked streams of strings.